1. Field of the Invention
The present invention relates generally to shoe inserts, and more particularly to podiatric orthotic devices ("orthoses") designed to provide functional control of lower extremity motion during gait.
2. Related Art
The surfaces of a typical shoe insole which support the heel and ball of the foot, which are the principal weightbearing areas of the foot, are approximately planar. Over the past several decades, research has disclosed that use of shoe inserts to modify the shape and resilience of these surfaces can provide many benefits. These benefits fall principally into two categories: stress accommodation and functional control. Inserts designed primarily to provide stress accommodation are called accommodative orthotic devices. Inserts designed primarily to provide functional control of lower extremity motion during gait are called functional orthotic devices.
An accommodative orthotic device is designed to distribute the stresses of weightbearing to areas of the foot which can best tolerate such stresses, in order to maximize comfort and minimize trauma to the sole of the foot. Such an orthosis provides a padded surface which may be flat, or which may be shaped to conform with the contours of a particular foot (a custom molded orthosis) or an average foot (a non-custom orthosis). Non-custom accommodative orthoses tend to be either significantly flatter than the average sole, or to be fabricated from a soft material which compresses under loads of less than about 5% of body weight so as to be tolerated across a population possessing wide variations in sole contour. Such devices may increase foot comfort, but are unlikely to provide significant control of foot motion.
A functional orthosis, on the other hand, is designed to guide and restrict the motion of joints of the foot in order to improve gait efficiency and to reduce the stresses imposed on lower extremity anatomical structures during gait. As a rule, functional orthoses are fabricated of firmer materials than are accommodative devices. The main goal of a functional orthosis is to resist pronation, a complex foot motion which produces the partial collapse of the medial longitudinal arch of the foot, best seen during the midstance phase of the gait cycle. Pronation actually consists of the abduction, eversion, and dorsiflexion of the forefoot in relation to the rearfoot. Because of the shapes and close contiguity of the joints involved, pronation is always accompanied by eversion of the heel and internal rotation of the leg and hip.
While pronation is a normal part of gait, it is now well established that excessive pronation is the source of many lower extremity pathologies, including muscle tiredness and inflammation, foot and knee joint pain, tendinitis, ligament strain, and even neurological damage. Excessive pronation also renders the gait less efficient since time and effort is wasted in collapsing (pronating) and recovering (supinating). It has been estimated that up to 70% of the population overpronates to some degree. Control of pronation is accomplished by a functional orthosis primarily by providing firm support for the foot's medial arch, secondarily by reducing heel eversion, and in some cases also by inverting the forefoot relative to the rearfoot.
Peak forces transmitted through the feet during running can easily exceed three times body weight. In order to resist such forces, a functional orthosis must be fabricated of a firm material. To remain comfortable and to avoid painful high pressure spots, it must also conform closely to the contours of the sole of the foot in its neutral position. Proper arch height is particularly critical in a functional orthosis. If the arch is too high, the device will be intolerably painful. On the other hand, if the arch is too low, control of pronation will be sacrificed. Significantly, due to the high forces transmitted through feet during gait, small variations in the form and material of orthoses can produce profound differences in orthosis function and comfort.
To satisfy the dual requirements of firm support and precisely contoured fit, prior art functional orthoses have generally been produced from a custom mold of an individual foot. In addition to the disadvantages of the tedium and expense of the custom-molding procedure, such prescription devices frequently require modifications subsequent to fitting.
With the exception of devices which employ an arch support consisting of a fluid-containing bladder, orthoses previously available which do not require a mold of the foot for their fabrication must be classified as accommodative, not functional devices. While such accommodative devices may increase foot comfort, they cannot reliably provide significant functional control since they are not typically made of sufficiently firm material and they do not conform equally well to the soles of different feet. A device sold without custom fitting is likely to have an arch which is too low to provide significant control of pronation.
Unfortunately, currently available functional orthoses are plagued by several additional shortcomings. First, these devices are typically bulky. To accommodate the orthosis, a shoe's insole, if present, must typically be removed or the shoe must be replaced with another of larger size. In either case, the fit of the shoe is altered. Moreover, insertion of such a device into the shoe raises the center of gravity of the foot within the shoe, thereby destablizing the foot. By changing the fit of the shoe, these devices frequently counteract its supportive design features.
Another disadvantage shared by currently available functional orthoses is that they are typically fabricated of rigid materials, e.g., hard plastics. Prolonged wear of such rigid devices causes degradation of the foot's plantar fat pad, leading to the formation of painful calluses.
Since the adverse effects of excessive pronation are suffered by a large percentage of the population, it would be highly desirable to have an orthotic shoe insert which could be readily accommodated in all types of footwear, which did not require custom fitting, and which provided effective functional control of pronation.